Molecular dynamics study of tryptophylglycine: a dipeptide nanotube with confined water.
To investigate the mechanism of structural changes of a peptide nanotube and water confined inside the channel, the helical peptide tryptophylglycine monohydrate (WG.H2O) was studied by molecular dynamics (MD) simulations using the three-dimension parallel MD program ddgmq (software package) and a consistent force field. Simulations were performed on both the water-containing system and a model system without water molecules. The details of the structural behavior with temperature are investigated for the entire simulated temperature range. Phase transitions were obtained at 115, 245, 270, 310, and 385 K, due to the contributions of both the peptide and the confined water subsystems. The crystalline, amorphous, liquidlike, liquid, and superheated phases of water were observed in the temperature ranges 40-115, 115-245, 245-310, 310-385, and >385 K, respectively. At 300 K, the diffusion constant of the confined water is 0.46 x 10-5 cm2 s-1, a value comparable to that of other peptide nanotubes. The empty peptide system melts at 440 K. Mechanisms of the negative thermal expansion (NTE) along the tube axis were investigated for different temperature ranges. The contraction of the crystalline water (or amorphous water) draws also the tube walls in and leads to NTE below 245 K. The other NTEs appear to be connected to the collapse of the ice network or the solid peptide network between 245 K and room temperature or from 310 to 440 K, respectively.
Pan
Yuansheng
Y
Laboratoire de Cristallographie, Ecole Polytechnique Fédérale de Lausanne, BSP, 1015 Lausanne, Switzerland, Swiss-Norwegian Beam Line, SNBL/ESRF, P.O. Box 220, F-38043 Grenoble, France, and Laboratoire des Matériaux Organiques à Propriétés Spécifiques, UMR CNRS 5041, Université de Savoie, 73376 Le Bourget du Lac, France.
Birkedal
Henrik
H
Pattison
Philip
P
Brown
David
D
Chapuis
Gervais
G